The NMR indirect nuclear spin–spin coupling constants for some small rigid hydrocarbons: molecular equilibrium values and vibrational corrections

Abstract

The indirect nuclear spin–spin coupling constants of allene and of two sterically strained hydrocarbons – cyclopropane and cyclopropene – calculated at different levels of electronic-structure theory are compared with each other and with experimental equilibrium constants, obtained from experiment by subtracting calculated vibrational contributions. It is found that, even in a relatively small basis set, the coupled-cluster singles-and-doubles (CCSD) method provides very good results, outperforming the other ab initio methods considered in this work – namely, the second-order polarization propagator approximation (SOPPA) and the multiconfigurational self-consistent field (MCSCF) approach. Calculations in the same basis set are also carried out at the hybrid level of density functional theory (DFT). Compared with the experimental equilibrium values the CCSD method gives the best results for the ab initio methods, while SOPPA consistently performs better than RASSCF. Hybrid DFT performs as well as SOPPA for the one-bond coupling constants, while, for the other constants, it provides results of similar quality as CCSD. The DFT approximation is also used to evaluate the indirect nuclear spin–spin coupling constants and their vibrational corrections for the larger cyclobutene and cyclobutane molecules.